It has been a while since I had the chance to delve in to Marion Clark so I have to get back to work and keep digging! Following my previous path I am now going to examine what Clark has to say about the first lumbar segment. As usual, I will start with some relevant anatomy.
The nerves associated with the first lumbar segment are: the ilioinguinal nerve (L1), the iliohypogastric nerve (L1), the genitofemoral nerve (L1-L2), the recurrent meningeal nerve, and the first lumbar sympathetic ganglion (which sends fibers to the renal plexus and the aortic plexus).
Some important muscles associated with the first lumbar segment are: the psoas, the diaphragm, multifidus, longissimus thoracis, and spinalis dorsi (there are other small muscles such as rotatores as well).
In the interest of being as direct as possible I will now move on to some considerations in relation to lesions of the first lumbar segment. The recurring theme that Clark provides is that a lesion (especially an extension lesion) is at first irritating to the segment and its associated neural connections however it then becomes inhibitory due to the related congestion caused by poor venous drainage through the smaller intervertebral formania. Related areas that are often affected are traceable through the associated nerves. There may be results seen through the abdominal wall all the way down to portions of the upper thigh and the genitals (this is why dermatomes are important!).
From a treatment perspective there is one muscle that continues to pop up as we examine the lumbar spine – the psoas muscle. I want to be clear that, for me (so far), this is quite possibly the single most important muscle in the body where Osteopathic treatments are concerned. Please do not misunderstand, all muscles are important all the time (as are all other tissues), however the psoas is such a powerful tool as it has such a wide ranging effect on so many tissues. The reason I bring this up in relation to the first lumbar segment is that the path of the nerves associated with L1 (and other lumbar segments) is either under or directly through the psoas muscle. If there is any compression or tension on the psoas muscle there is an obvious reflex loop set up through the related alteration to the nerves, arteries, veins, and lymphatics that pass through or under the psoas. Also, from a simple mechanical standpoint, the psoas is a major contributor to the static positioning and dynamic function of the pelvis and the lumbar spine. This one muscle essentially has a dominating impact on the entire lower body. In my eyes, due to the psoas, the leg actually starts at T12 (while I am not a high level Osteopathic scholar or researcher I do feel this to be an important idea that I would like to put up for discussion and criticism).
Getting back to Marion Clark’s work, it is important to note that reproductive functions essentially begin at L1 from a neural standpoint. When considering the relationship between structure and function it can be posited that fertility or sexual issues should be considered from L1 downwards. There is the possibility of referred pain in the pelvic region due to stimulation of the efferent nerves from L1.
To add some more thoughts to the discussion of L1 and the psoas I think it is important that there is a lot of non-invasive visceral work performed by the psoas if used properly (not just in a mechanical sense, also in a neural and fluid flow sense). Also I would like to mention that the psoas can be directly affected by the diaphragm (and vice versa) due to their direct connections to L1 (the erector muscles also have reflexive possibilities at this level). The final point I would like to make is that the primary movement characteristics of L1 are flexion/extension however it is very important to note that there is a lot of rotational stress due to the transition occurring at the thoraco-lumbar junction.
A lot of food for thought as I finish up the lumbar segments!